Our invention is an apparatus for preventing jackknifing in an undesired direction in an articulated vehicle, which has a locking unit inserted between the front part and the trailer of the articulated vehicle. The locking unit is operably connected to a control apparatus the input signals of which are provided by the wheel steering angle, and the change in angle of articulation in the other direction.
There are anti-jackknife devices known for preventing jackknifing of saddle-type tractor-trailers, in which there is a double-acting hydraulic working cylinder between the tractor and semi-trailer. The piston of the cylinder is arranged from the tractor and the working cylinder is attached to the element of the saddle-type connecting device which rotates with the trailer. The two working chambers of the double-acting working cylinder are connected with a passage in which a valve unit is arranged (as is described e.g. in U.S. Pat. No. 2,692,146).
When the valve unit is closed, the hydraulic fluid cannot pass between the two working chambers, and then the relative angle between the two parts of the vehicle remains constant, i.e. the vehicle cannot jackknife.
The hydraulic fluid can pass between the two working chambers, when the valve unit is open and the angular disposition of the two vehicle parts can change and the anti-jackknifing unit will not prevent such change.
Various solutions are known for the control of the valve unit, which influence the control of the valve unit through sensing various vehicular parameters or passage-dynamical characteristics or a plurality of characteristics, respectively.
There are solutions known in which the control valve unit is in connection with the braking system of the vehicle and a jackknife-preventing effect is created during braking, such as in the apparatus described in British Pat. No. 1,240,554.
In a further proposed solution according to British Pat. No. 1,291,858 the valve of the liquid passage connecting the working chambers of the double-acting hydraulic working cylinder, is mechanically connected to the steering mechanism; with an open valve position corresponding to wheels when they are steered to one side.
The joint effect of a plurality of driving-dynamical factors contributes to the formation of a jackknifing condition in articulated vehicles. The aforesaid two British patents take into consideration only one selected factor each, therefore, other than in the case of braking and sideways steering, respectively, they do not prevent jackknifing.
These devices have not found any widespread application in practice.
There is also known from West German published patent application No. 2,420,203 a rear axle-driven articulated bus, in which the control unit of the valve of the hydraulic working cylinder that hinders jackknifing, has two sensors, one of them sensing the steering angle and the other the angle of articulation of the two vehicle units. A permitted maximum angle of articulation corresponding to a given angle of turn of steering, is stored in the control unit. A comparing unit compares the sensed and permitted angles of articulation, and when the latter is exceeded the control unit closes the valve of the hydraulic working cylinder, i.e. fixes the anti-jackknife apparatus.
The aforementioned West German device--which in our view is the most developed one--is truly capable of setting a suitable limit for the size of the jackknifing angle thus it prevents a dangerous degree of overarticulation of the vehicle onto itself. A not lesser dangerous operating condition--especially in the case of rear axle drives--is the acceleration in a sharp curve, because in this case a considerable part of the friction that is available on the rear axle, is consumed by the diving moment and thus the rear axle is not capable of countering the centrifugal force. The trailer part then proceeds in the direction of straightening out and then articulates into the opposite direction. This phenomenon is especially dangerous for the traffic in the adjacent lane, especially, because this phenomenon cannot be directly sensed by the driver. (He can immediately sense the slippage of any axis of the tractor, and can compensate for that.)
In addition to the prevention of overarticulation and irregular straightening out, our aim in creating the invention was also to bring about a highly reliable, low cost apparatus which still performs its function accurately.
In creating the device of the invention it was our aim to provide such an angle of articulation-affecting apparatus which prevents jackknifing when the vehicle breakes in a straightaway or in a curve, prevents the swerving of the trailer in a curve, and prevents the special kind of jackknifing which occurs especially in the case of trailers with driven shafts.
The apparatus of the invention prevents only that kind of articulation, the direction of which does not correspond to the sum of the steering angle and of the angle of articulation in the direction determined by the slippage-free progress of the wheels of the vehicle.
I. Our invention is an apparatus for articulated vehicles for preventing articulation in an extraordinary direction, having a locking means connected to the parts of the vehicle that are connected by the articulating hinge, the locking means being operatively connected to an angular position evaluating unit for evaluating the angle of articulation which deviates from a predetermined angle of articulation that corresponds to the steered angle of the front wheel, which unit is arranged with the sensor for the steered angle of the front wheels of the front part of the vehicle and the sensor for the angle of articulation. The evaluating unit is connected to the actuating unit of the articulation locking means, one entering signal of which is the deviation signal determined by the exit signal of the angle evaluating unit, the deviation signal--according to choice--is positive at that angle of articulation (.beta.), at that angle of wheel steering (.alpha.) to which an angle of articulation (.beta.p) belongs, that is to the right when looking down at the vehicle in the direction of its progress, and is negative at that angle of articulation (.beta.) which is at the angle of articulation (.beta.p) belonging to a steered angle (.alpha.) that is to the left; the other input signal of the operating unit of the locking means is formed by the prefix of the exit signal of the angle-of-articulation direction signaler which--according to choice--is positive at that direction of change in angle of articulation at which when viewed from above, the articulation of the trailer part to the front part is in a clockwise direction, and is negative at that direction of change of angle of articulation at which the articulation of the trailer part to the front part is counterclockwise, and the locked position of the articulation locking means corresponds to the two opposed sign signals of the locking actuating unit. In the angular position evaluating unit the exit signal suitably corresponds to the angle of articulation (.beta.) which lies outside the angle domain (.DELTA..beta.) which includes the angle of articulation (.beta.p) corresponding to the steered angle (.alpha.) of the front wheel. PA0 II. In a suitable embodiment of our invention the articulation locking means is formed as a piston-operated hydraulic working mechanism the two operating chambers of which are connected to the locking actuating unit by means of hydraulic lines; the actuating unit for the locking mechanism is formed by a three position, four-path direction-changing valve as well as an inner hydraulic loop which contains a check valve; the first working chamber is connected by a hydraulic line to the first connection of the four-path, three-position direction-changing valve, the second working chamber is connected by a hydraulic line to its second connection, and an inner hydraulic loop is connected to its third and fourth connections with a check valve closing off flow from the direction of the third connection towards the fourth one; in the resting center position of the piston of the three-position, four-path direction-changing valve at least the first, second and fourth connections are open to each other, in positively driven position the first and fourth connections, as well as the second and third connections, and in negatively driven position the first and third positions as well as the second and fourth positions, respectively, are connected to each other; the articulation locking means simultaneously forms the articulation direction-giving means by the open position of the check valve forms a positive output signal when the three-position, four-path direction-changing valve is in a positive position, and when the three-position, four-path direction-changing valve is in a negative position then it forms a negative output signal, the closed position of the check valve provides in the positive position of the three-position, four-path direction-changing valve a negative output, and in the negative position of the three-position, four-path direction changing valve it forms a positive output signal. PA0 III. In a further preferred embodiment of our invention the angular position-evaluating unit is formed by a spring arranged between the sensing piston connected to the transmitting element of the steering signaler and an end of the piston of the three-position, four-path direction-changing valve, as well as a spring arranged between the sensing piston supported by the cam formed on the guidance rod connected to the transmitting element of the articulation angle signaler, and this sensing piston, and the other end of the three-position, four-path direction-changing valve. PA0 IV. In a further advantageous embodiment of our invention the angular position-evaluating unit is provided by a cam formed on a rotating segment, a cam formed on a rotating segment connected to the connecting element of the angle of articulation signaler, a difference-formng arm which is supported through sensors by the above and is disposed in an axially movable manner on a slide valve that has a limited possibility of movement between abutments, said arms being arranged between abutting terminal elements and being supported by a spring and mounted rotatably about a slide, and a three-position, four-path direction changing valve and its slide valve which is in motion transmitting connection with the aforesaid slide valve.
In the interest of the satisfactory operation of the hydraulic system it is under constant initial pressure through the container of the liquid, suitably by the aid of the pneumatic braking system of the vehicle.